A network is used to couple a host server computer to one or more client computers, using wires (including telephone wires), fiber optics, or wireless signals. There are at least several million computers in the United States alone, and an increasing number of these computers are becoming network-accessible.
FIG. 1 depicts a generic network 10 that includes a server 20 and one or more client computers or workstations 30, 30' that each include a central processing unit ("CPU") 40, 40'. (As used herein, the term computer shall be understood to include the term workstation.) The server and clients communicate over information paths 50, 50' that, as noted, may be wires, optical cables, or radio transmissions. Paths 50, 50' may be parallel, e.g., a plurality of wires, or may be serial, e.g., a single data line. At the client end, each computer includes a network interface circuit 60, 60'.
Network interface controller 60, 60' typically is an integrated circuit ("IC") chip that provides interfacing between the client computer and the remote host/server. According to current Ethernet network protocol, networked computers rely upon three attributes of the network: (a) the network is always up or active, (b) the client computer is always alive and coupled to the network, and (c) and/or application programs may be run locally or run remotely over the network from another computer. Each computer 30, 30' includes a power supply that is typically coupled to 110 VAC/220 VAC, and whose output DC voltages are coupled through an ON/OFF power switch relay, here depicted as a manually operated switch S1, or S1'. If the computer is to communicate with the network, the power switch is ON, otherwise there is no operating voltage to the computer. Although S1 is depicted as a manually operated switch, it is understood that power may be switched on or off using other switching devices, including electronic switching devices.
A single desktop computer such as computer 30 or 30' may only consume perhaps 150 watts of electrical power. However, cumulatively the electrical power consumed by all of the computers in the United States, and indeed in the world, is becoming appreciable. With a view to reducing this power consumption and the environmental cost involved in generating the power, the United States Federal Government has promulgated the Energy Star program.
As applicable to the present invention, the Energy Star program requires that computers be powered-off to a low energy state of less than 30 watts consumption during periods of inactivity. Computers meeting this requirement, so-called "green PCs", are permitted to bear an Energy Star insignia. Conversely, non-Energy Star compliant equipment is often less well received in the commercial marketplace.
One approach to complying with the Energy Star requirement is to design lower power consumption equipment, laptop computers, for example. Many computers can also benefit from advanced power management features, including features that are incorporated into the computer operating system. Intel Corp. and Microsoft Corp. collectively have promulgated one such Advanced Power Management specification.
Using power management, a computer can power-down its harddisk and slow its CPU clock rate, thus saving electrical power, after inactivity exceeding a certain threshold. Depressing a key on the computer keyboard, or moving a mouse or other control device will "awaken" the computer, restoring it to full CPU clock rate and/or reactivating the hard disk, within a few seconds.
However, powering-off a networked Energy Star compliant computer during periods of inactivity detrimentally interrupts established events that constantly occur in a networked computing environment, polling for example. In practice, powering-off a networked computer could readily make such a computer a pariah in the network marketplace. It is thus desirable to maintain some operating power, preferably less than 30 watts, to a networked computer to permit the computer to respond to the network without being manually awakened.
It is known in the art to remotely awaken a powered-off computer with a facsimile ("FAX") signal or a modem signal coupled to the computer's serial port from the telephone line. However such "awakening" requires a FAX or modem signal to be sent to the specific telephone number associated with the computer's modem. The modem must be powered at all times and may consume from 5 watts to 10 watts power.
Thus, there is a need to make a networked computer Energy Star complaint, without risk of interrupting network functions that can occur even during periods of client-system inactivity. Preferably the computer should be capable of being powered-off, and then "awakened" using only signals available from the network and coupled to the network interface card. Further, there is a need for a mechanism or system by which a large number of networked computers can be powered-on, quickly or even simultaneously.
The present invention discloses a method and apparatus for accomplishing these needs.